The toad urinary bladder, a widely used model for the human renal tubule, has the same salt and water conservation functions, and responds to the same regulating hormones (aldosterone and antidiuretic hormone) and drugs which affect human salt and water metabolism. Aldosterone is thought to stimulate sodium transport by inducing new protein synthesis; antidiuretic hormone (ADH) is thought to stimulate both sodium and water transport by an intermediate, cyclic adenosine-3', 5'-monophosphate (cAMP). However, neither a specific aldosterone-induced protein (AIP), or a rapidly-responsive ADH- or cAMP-sensitive membrane component has been demonstrated. This project combines electrophysiological and biochemical investigations of salt and water transport across the toad bladder. The proposed AIP, demonstrated in our preliminary experiments, will be isolated and characterized; the ADH- and/or cAMP-sensitive molecules will be sought by similar means. Hypotheses will be tested by physico-chemical techniques designed to clarify the basis for hormone and drug action. Measurements will include: electrical potential difference; short-circuit current; transepithelial resistance; osmotic water flow; isotope flux; radiotracer incorporation into proteins and nucleic acids; gradient slab gel and high voltage electrophoresis; chromatography; and autoradiography. Physico-chemical variables will include: ion and non-electrolyte composition, enzymes, hormones, drugs, pH and osmotic pressure. Ion selectivity sequences will be established for each isolated molecule. These studies will increase our understanding of normal and abnormal hormonal control mechanisms, particularly those associated with cardiac and renal disease, and will permit the development of new therapeutic agents for their treatment.